Method for applying a low residual stress damping coating

ABSTRACT

A method for applying a low residual stress damping coating to a surface of a substrate is provided. The method includes heating a ferromagnetic damping material in powder form such that the ferromagnetic damping material is at least partially molten. Next, the at least partially molten ferromagnetic damping material is directed at a surface of the substrate at an application velocity so that it adheres to the surface of the substrate to create a ferromagnetic damping coating on the surface of the substrate, resulting in a coated substrate. The ferromagnetic damping coating has a balanced coating residual stress, including a tensile quenching stress component and a compressive peening stress component. The balanced coating residual stress is within a range of ±50 MPa without having to subject the coated substrate to a high temperature annealing process. The resulting coated substrate exhibits a high damping capacity.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.11/736,093, filed Apr. 17, 2007, which is a continuation-in-part of U.S.application Ser. No. 11/215,195, filed Aug. 30, 2005, now abandoned,which claimed priority to and the benefit of U.S. ProvisionalApplication No. 60/606,890, filed Sep. 3, 2004, the entire contents ofwhich are hereby incorporated by reference. Moreover, the entiredisclosure provided in Applicant's U.S. Patent Application PublicationNo. 2008/0124480, published on May 29, 2008, is hereby incorporated byreference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Part of the invention herein described was made in the course of orunder a contact with the U.S. Department of the Navy.

TECHNICAL FIELD

The present disclosure relates to coatings applied to a surface of asubstrate. More specifically, the present disclosure is directed to amethod for applying a low residual stress damping coating to a surfaceof a substrate.

BACKGROUND OF THE INVENTION

Engineering components, particularly rotating components such as turbinefan blades, compressor blades, impellers, blisks, and integrally bladedrotors (IBRs), commonly encounter vibrational stresses in operation.These vibrational stresses can fatigue the component and eventuallycause the component to fail. In order to prevent component failure,researchers have investigated a number of approaches for attenuating thevibrations that develop under cyclic loading. Such approaches haveincluded dry friction dampers, tuned-mass or particles, air cavities,shape memory alloys, viscoelastic dampers, and ceramic coatings.

Another approach that has been considered for vibration damping is theapplication of a thin coating of a ferromagnetic material on a surfaceof a substrate. In particular, Fe—Cr based ferromagnetic materialscomprising about 16% (by weight) chromium (Cr), either about 1% to about6% aluminum (Al) or about 1% to about 4% molybdenum (Mo), and thebalance iron (Fe), have been shown to exhibit high damping, as well asgood mechanical strength and corrosion resistance. As a result, theFe—Cr based ferromagnetic materials are considered well-suited forapplications involving severe and hostile operating conditions, such asthose experienced by turbine components.

As mentioned, Fe—Cr based ferromagnetic materials have been shown topossess a high damping capacity. These ferromagnetic materials includemagnetic domains, which are separated by magnetic domain walls. When theferromagnetic material is exposed to external magnetic fields orstresses, the magnetic domain walls can move. When the movement of themagnetic domain walls is irreversible, a portion of the energy providedto the ferromagnetic material is dissipated as internal friction. Thisdamping mechanism is commonly referred to as magneto-mechanical damping.

Thus, high damping in ferromagnetic materials is achieved due to theirreversible movement of the magnetic domain walls. If movement of themagnetic domain walls is constrained or hindered, the ferromagneticmaterial will not exhibit any appreciable damping. Unfortunately,conventional coating processes create large residual stresses that actas obstacles to the movement of the magnetic domain walls. For example,in a conventional air plasma spray process, the residual stress isdominated by tensile quenching stresses; while in a conventional coldspray process, the residual stress is dominated by compressive peeningstresses. As a result, a ferromagnetic coating applied to a substrate byconventional coating processes will provide no significant damping. Inorder to free up the movement of the magnetic domain walls, the commoncourse of action is to subject the coated article to a high temperatureannealing process. For example, a suggested process comprises annealingin high vacuum at temperatures between 700° C. and 1200° C. for 30minutes to 6 hours, followed by furnace cooling at 120° C./h.

The high temperature annealing process is a critical drawback that hashindered the use of ferromagnetic materials in real world applications.For example, high temperature annealing of geometrically complexstructural components, such as gas turbine engine components, can causemicrostructural defects, decomposition and precipitation in componentsubstrate materials, and most importantly can warp or deform thestructural component rendering the component unfit for its intended use.

Thus there is a need in the art for a process capable of depositing acoating comprising a ferromagnetic damping material on a surface of asubstrate that exhibits a high damping capacity without having toundergo a high temperature annealing process. The presently disclosedmethod satisfies this need.

SUMMARY OF THE INVENTION

In its most general configuration, the presently disclosed method forapplying a low residual stress damping coating advances the state of theart with a variety of new capabilities and overcomes many of theshortcomings of prior methods in new and novel ways. The method forapplying a low residual stress damping coating overcomes theshortcomings and limitations of the prior art in any of a number ofgenerally effective configurations.

The present disclosure relates to a method for applying a low residualstress damping coating on a surface of a substrate. The method providesa technique for increasing the damping of a substrate having a substratethickness. Generally, the method includes heating a ferromagneticdamping material in powder form such that the ferromagnetic dampingmaterial is at least partially molten. Next, the at least partiallymolten ferromagnetic damping material is directed at a surface of thesubstrate at an application velocity such that the at least partiallymolten ferromagnetic damping material adheres to the surface of thesubstrate. The ferromagnetic damping material then cools tosolidification within a solidification period to create a ferromagneticdamping coating on the surface of the substrate, resulting in a coatedsubstrate.

The ferromagnetic damping coating has a balanced coating residualstress, which includes at least a tensile quenching stress component anda compressive peening stress component. In general, the balanced coatingresidual stress is within a range of ±50 MPa without the coatedsubstrate ever being subjected to an annealing temperature of above 700°C. for an annealing period of longer than 30 minutes. The ferromagneticdamping coating may have a coating thickness of about 2% (or about 1% oneach side of the substrate) to about 20% of the substrate thickness. Theresulting coated substrate has a damping loss factor of at least3.6×10⁻³ at a strain amplitude of 0.0466×10⁻⁴ to 7.77×10⁻⁴.

The presently disclosed method thus provides the ability to deposit acoating comprising a ferromagnetic damping material on a surface of asubstrate that exhibits a high damping capacity without having toundergo a high temperature annealing process.

BRIEF DESCRIPTION OF THE DRAWINGS

Without limiting the scope of the claimed method for applying a lowresidual stress damping coating, reference is now given to the drawingsand figures:

FIG. 1 is a cross-sectional view of a substrate with a low residualstress ferromagnetic damping coating applied to a surface thereof, notto scale;

FIG. 2 is a schematic of a spray torch applying a low residual stressferromagnetic damping coating on a surface of a substrate, not to scale;

FIG. 3 shows a graph of the system loss factor versus max strain at thesecond bending mode for three beams coated by different processes;

FIG. 4 shows a graph of the system loss factor versus max strain at thethird bending mode for three beams coated by different processes; and

FIG. 5 shows a graph of the system loss factor versus max strain at thefourth bending mode for three beams coated by different processes.

DETAILED DESCRIPTION OF THE INVENTION

The presently disclosed method for applying a low residual stressdamping coating enables a significant advance in the state of the art.The preferred embodiments of the method accomplish this by new and novelarrangements of elements and steps that are configured in unique andnovel ways and which demonstrate previously unavailable but preferredand desirable capabilities. The description set forth below inconnection with the drawings is intended merely as a description of theembodiments of the claimed method, and is not intended to represent theonly form in which the method may be constructed, carried out, orutilized. The description sets forth the designs, functions, means, andmethods of implementing the method in connection with the illustratedembodiments. It is to be understood, however, that the same orequivalent functions and features may be accomplished by differentembodiments that are also intended to be encompassed within the spiritand scope of the claimed method.

With reference now to FIG. 1, a cross-sectional view of a substrate (20)having a low residual stress ferromagnetic damping coating (10) appliedto a surface (24) of the substrate (20) is shown. Preferably, theferromagnetic damping material utilized to create the low residualstress ferromagnetic damping coating (10) comprises a Fe—Cr basedferromagnetic damping material comprising about 16% (by weight) chromium(Cr), either about 1% to about 6% aluminum (Al) or about 1% to about 4%molybdenum (Mo), and the balance iron (Fe). However, other ferromagneticdamping materials may be successfully utilized, including, but notlimited to, Co-(22-38 wt %)Ni and Fe-(11-22 wt %)Mn. The substrate (20)may comprise a turbine component, such as a fan blade, compressor blade,impeller, blisk, or integrally bladed rotor, just to name a few. Theturbine component may be formed of virtually any metal including, butnot limited to, titanium, titanium-based alloys, steel alloys, nickel,nickel-based alloys, aluminum, and aluminum-based alloys. As usedherein, the term “turbine” may refer to gas turbines, steam turbines,water turbines, wind turbines, or any other type of turbine orcomponents thereof that experience vibrational stresses.

With reference now to FIG. 2, an embodiment of a method for applying alow residual stress ferromagnetic damping coating (10) to a surface (24)of a substrate (20) will be described. As seen in FIG. 2, a spray torch(30) for applying the low residual stress ferromagnetic damping coating(10) is directed at the surface (24) of the substrate (20). The spraytorch (30) preferably comprises a high velocity oxygen fuel (HVOF) typetorch, such as those used in connection with the Praxair-Tafa JP-5000HVOF spray system and Jet Kote spray systems. In a HVOF spray system, amixture of fuel (F) and oxygen (O) is fed to the spray torch (30) wherethe mixture is combusted. A coating material in powder (P) form is fedto the spray torch (30) where the powder (P) particles are entrained bythe combustion gases and undergo heating and acceleration as they travelthrough and exit the spray torch (30). The spray torch (30) may besupplied with cooling water (CW) to help control the temperature of theprocess.

The presently disclosed method provides a technique for increasing thedamping of a substrate (20) having a substrate thickness (22). In oneembodiment, the method includes heating a ferromagnetic damping materialin powder form such that the ferromagnetic damping material is at leastpartially molten. The heating step may be accomplished in the spraytorch (30) from the hot combustion gases as described above. To ensurethat the ferromagnetic damping material is at least partially molten, itis preferable to heat the ferromagnetic damping material to, or near,its melting point.

Next, the at least partially molten ferromagnetic damping material isdirected at a surface (24) of the substrate (20) at an applicationvelocity. The application velocity is such that the at least partiallymolten ferromagnetic damping material adheres to the surface (24) of thesubstrate (20). After the at least partially molten ferromagneticdamping material adheres to the surface (24) of the substrate (20), itcools to solidification within a solidification period to create aferromagnetic damping coating (10) on the surface (24) of the substrate(20), thus forming a coated substrate (100). The solidification periodis relatively rapid, generally less than a few seconds.

The key aspect of the method lies in the fact that the resultingferromagnetic damping coating (10) has a balanced coating residualstress. The balanced coating residual stress includes at least a tensilequenching stress component and a compressive peening stress component.The tensile quenching stress component is contributed by the cooling andcontraction of the at least partially molten ferromagnetic dampingmaterial on the surface (24) of the substrate (20). On the other hand,the compressive peening stress component is induced by the at leastpartially molten ferromagnetic damping material impacting the surface(24) of the substrate (20), or coating (10), at high velocity causing aslight plastic deformation of the substrate (20) or coating (10). It hasbeen appreciated that by carefully controlling the applicationtemperature and the application velocity of the ferromagnetic dampingmaterial, the compressive peening stress component may be increased andthe tensile quenching stress component may be decreased. As a result,the ferromagnetic damping coating (10) has a balanced coating residualstress, where the compressive peening stress component and the tensilequenching stress component effectively cancel, or balance, one anotherto provide the balanced coating residual stress.

This discovery has enabled the ability to apply a ferromagnetic dampingcoating (10) on a surface (24) of a substrate (20) that achieves highdamping without having to subject the coated substrate (100) to a hightemperature annealing process, such as annealing at an annealingtemperature of above 700° C. for an annealing period of longer than 30minutes, followed by a controlled furnace cooling. The high damping is adirect result of the ferromagnetic damping coating's (10) balancedcoating residual stress, which is believed to create a substantiallysmaller amount of obstacles (i.e., pinning sites) that hinder themovement of the magnetic domain walls within the ferromagnetic dampingcoating (10). Applicant has found that a balanced coating residualstress within a range of ±50 MPa (with positive values representing atensile residual stress and negative values representing a compressiveresidual stress) allows a high level of damping in the ferromagneticdamping coating (10). As used herein, the phrase “balanced coatingresidual stress” refers to a residual stress of the coating (10) withina range of ±50 MPa. As a result of the discovery of the balanced coatingresidual stress, geometrically complex structural components, such asgas turbine components, may be damped with a ferromagnetic dampingcoating (10) without suffering the drawbacks associated with the hightemperature annealing process.

In a particular embodiment, the at least partially molten ferromagneticdamping material is directed at the substrate at an applicationtemperature of at least 800° C. and at an application velocity of atleast 450 m/s. These application parameters provide a delicate balancebetween the thermal and kinetic energy imparted upon the ferromagneticdamping material to obtain a balanced coating residual stress within the±50 MPa range to achieve a high level of damping from the ferromagneticdamping coating (10).

Generally, the ferromagnetic damping coating (10) is applied as a thinlayer. Applicant has found that applying a ferromagnetic damping coating(10) having a coating thickness (12) of about 2% to about 20% of thesubstrate thickness (22) allows the ferromagnetic damping coating (10)to provide damping without having an adverse effect on the substrate(20). For example, when the substrate (20) comprises a component of agas turbine, a coating thickness (12) that is too large can decrease theefficiency and operability of the gas turbine component. In oneembodiment, the ferromagnetic damping coating (10) may be deposited oneside of the substrate (20); while in other embodiments, theferromagnetic damping coating (10) may be deposited on more than oneside of the substrate (20). As used herein, coating thickness (12)refers to the total thickness of the ferromagnetic damping coating (10)applied to the substrate (20).

As will be seen in the example presented below, the coated substrate(100) resulting from the presently disclosed method has a higher levelof damping compared to substrates that are coated using conventionalcoating processes. In general, the coated substrate (100) resulting fromthe presently disclosed process was found to have a system loss factor(i.e., damping loss factor) of at least 3.6×10⁻³ at strain amplitude ofbetween 0.0466×10⁻⁴ to 7.77×10⁻⁴.

To illustrate the effectiveness of the method, reference will now bemade to an example. In this example, a Praxair-Tafa JP-5000 HVOF spraysystem was utilized to carry out the method. The ferromagnetic dampingmaterial utilized was Fe-16Cr-3Mo. The substrate (20) comprised aTi-6Al-4V beam having dimensions of 8.0 in×0.75 in×0.090 in. Oxygen at asupply pressure of 210 psi was fed to the spray torch (30) at a flowrate of 1800 scfh with a pressure of 123±5 psi. The fuel comprisedkerosene at a supply pressure of 170 psi, and was fed to the spray torch(30) at a flow rate of 5.1 gallons/hour with a pressure of 108±5 psi.The combustion pressure was maintained at 94±5 psi. The powderedferromagnetic damping material was injected to the spray torch (30) viaa powder feeder speed of 270 rpm and a nitrogen carrier gas at a flowrate of 22±2 scfh at a supply pressure of 50 psi. Cooling water wassupplied to the spray torch (30) at a temperature of 56±5° F. and exitedthe spray torch (30) at a temperature of 102±5° F.

The spray torch (30) was positioned from the surface (24) of thesubstrate (20) at a standoff distance of 14 inches, and theferromagnetic damping material was deposited on the surface (24) of thesubstrate (20) at a damping material deposition rate of about 76±5grams/minute. In this particular example, each side of the substrate(20) beam was coated with the ferromagnetic damping material with acoating thickness (12) of about 0.004-0.005 inch per side, resulting ina coating thickness (12) to substrate thickness (22) ratio of about 8%to about 10% (or about 4% to about 5% each side).

For purposes of comparison, two additional Ti-6Al-4V beams were coatedwith the same ferromagnetic damping material using a conventional coldspray process and a conventional air plasma spray process. The twoadditional Ti-6Al-4V beams had the same dimensions as the substrate (20)noted above, as well as the same coating thickness (12).

Turning now to FIGS. 3-5, the vibration damping associated with each ofthe three separately coated beams (presently disclosed process,conventional cold spray process, and conventional air plasma sprayprocess) is depicted graphically in terms of the system loss factor (η)versus max strain (ε). Each coated beam was cantilever clamped on a highpower vibration shaker. Frequency response functions for each coatedbeam were measured utilizing an accelerometer and a laser-vibrometer formeasuring the velocity or displacement of a point on the coated beam.The system loss factor (i.e., damping loss factor) was calculated usingthe half-power bandwidth method. According to the half-power bandwidthmethod, a reference point on the frequency response function of √{squareroot over (2)}/2, or 0.707, of the maximum amplitude is chosen. Thisamplitude crosses the frequency response function at two differentfrequencies, with the difference between these two different frequenciesbeing the half-power band. The relationship between the half-power bandand the frequency of the maximum amplitude (i.e., resonant frequency) isthe measurement of the system loss factor (η), which can be seen by thefollowing equation:

$\eta \approx \frac{{half}\text{-}{power}\mspace{14mu} {band}}{{resonant}\mspace{14mu} {frequency}}$

The strain on each coated beam was determined via finite element methodto correlate the displacement of the coated beam at a point to thestrain at the root of the coated beam. The actual displacement at aspecific point was then calculated from the measured velocity at thatpoint while vibrating in a resonant mode. The following equation wasused to calculate the displacement:

d=v/(2πf)

where “v” is the measured velocity of the coated beam at a point and “f”is the measured resonant frequency.

The strain at any point on the coated beam can then be determined fromthe calculated displacement of the coated beam and the mode shape. Forthe graphs shown in FIGS. 3-5, the coated beams were excited incantilever bending modes (i.e., second bending mode, third bending mode,and fourth bending mode) and the data is referred to in terms of the maxstrain amplitude in the mode shape, which occurs at the root of thespecimen. Using the finite element method, it is possible to find aconversion factor between observed displacement and root strain.

As seen in FIGS. 3-5, the system loss factor (i.e., damping loss factor)of the beam coated with the presently disclosed process (i.e., “lowstress process”) is significantly higher than the beams coated via theconventional cold spray and air plasma spray processes in each of thesecond, third, and fourth bending modes. In fact, the system loss factorof the beam coated by the “low stress process” was about 300-1000%higher than the beams coated by the conventional cold spray and airplasma spray processes. It is important to note that the system lossfactor is independent of the vibratory mode of coated substrates. As aresult, the ferromagnetic damping coating is capable of enhancingdamping significantly at almost all the vibration modes of the coatedsubstrate.

In FIG. 3, the lowest value of the system loss factor observed at thesecond bending mode for the “low stress process” was 5.9×10⁻³ at a maxstrain amplitude of 0.227×10⁻⁴, while the highest value of the systemloss factor was 16.9×10⁻³ at a max strain amplitude of 3.51×10⁻⁴. Incomparison, the highest values of the system loss factor at the secondbending mode for the cold spray process was 2.0×10⁻³ at a max strainamplitude of 8.56×10⁻⁴, and for the air plasma spray process was2.22×10⁻³ at a max strain amplitude of 6.78×10⁻⁴. As can be appreciated,the “low stress process” resulted in a significantly higher level ofdamping when compared to the conventional cold spray and air plasmaspray processes. In fact, the highest level of damping observed for thecold spray and air plasma spray processes were each less than half ofthe lowest level of damping observed for the “low stress process.”

Similar results were obtained for the third bending mode, as seen inFIG. 4. The lowest value of the system loss factor observed for the “lowstress process” was 5.72×10⁻³ at a max strain amplitude of 0.0568×10⁻⁴,while the highest value of the system loss factor was 14.3×10⁻³ at a maxstrain amplitude of 2.44×10⁻⁴. On the other hand, the highest observedsystem loss factor for the beam coated with the conventional cold sprayprocess was 1.60×10⁻³ at a max strain amplitude of 7.19×10⁻⁴, and thehighest system loss factor for the beam coated with the air plasma sprayprocess was 3.28×10⁻³ at a max strain amplitude of 10.25×10⁻⁴. Again,for the third bending mode, the lowest value of the system loss factorfor the “low stress process” was still significantly higher than thehighest value of the system loss factor for the beams coated by the coldspray and air plasma spray processes.

Still further promising results were obtained with respect to the fourthbending mode, as seen in FIG. 5. For the fourth bending mode, the lowestvalue of the system loss factor observed for the “low stress process”was 3.6×10⁻³ at a max strain amplitude of 0.0466×10⁻⁴, while the highestvalue of the system loss factor was 17.9×10⁻³ at a max strain amplitudeof 3.88×10⁻⁴. On the other hand, the highest observed system loss factorfor the beam coated with the conventional cold spray process was1.91×10⁻³ at a max strain amplitude of 3.52×10⁻⁴, and the highest systemloss factor for the beam coated with the air plasma spray process was3.13×10⁻³ at a max strain amplitude of 7.77×10⁻⁴. As with the second andthird bending modes, at the fourth bending mode the lowest value of thesystem loss factor for the “low stress process” was still higher thanthe highest value of the system loss factor for the beams coated by thecold spray and air plasma spray processes.

Although the example discussed utilized a Praxair-Tafa JP-5000 HVOFspray system, those with skill in the art will appreciate that otherspray systems capable of achieving the preferred parameters of themethod may be successfully implemented. Applicant has performed themethod utilizing a Jet Kote spray system with the following operatingparameters: Powder feeder speed of 4 rpm; Oxygen flow rate of 445 scfhat 60 psi; Hydrogen (fuel) flow rate of 1040 scfh at 70 psi; Argon(powder carrier gas) flow rate of 25 scfh at 100 psi; Damping MaterialDeposition Rate of 30 grams/minute; and a standoff distance of 10inches.

The presently disclosed method may be utilized to apply a layer offerromagnetic damping coating (10) having a balanced coating residualstress to any number of substrates (20) to provide high damping withouthaving to perform a high temperature annealing process. Such substrates(20) may include fan blades, compressor blades, impellers, blisks, andintegrally bladed rotors (IBRs), just to name a few.

It is well known that when titanium and titanium alloys are subjected toa high temperature heat treatment, an oxygen-enriched layer, known asalpha case, will form on the surface of the titanium or titanium alloy.The alpha case is generally much harder and more brittle than thetitanium or titanium alloy. For example, the alpha case layer generallyhas a Vicker's hardness number ranging from about 500 to 600, while thebulk hardness (i.e., the interior hardness) of the titanium or titaniumalloy ranges from about 200 to 350. Depending on the temperature and theamount of time of the heat treatment, the alpha case layer thickness maybe within a range from about 25 μm to about 200 μm. Moreover, a titaniumor titanium alloy component that has been coated may still besusceptible to the formation of an alpha case layer. This can occur whenoxygen diffuses through the coating layer and into the titanium ortitanium alloy substrate microstructure just below the interface createdbetween the coating layer and the surface of the titanium or titaniumalloy substrate.

For many applications, an alpha case layer is highly undesirable becauseit has reduced fatigue resistance and tends to create a series ofmicrocracks, which can reduce the metal's performance and cause failure.Generally, before the heat treated titanium or titanium alloy isutilized, the layer of alpha case must be removed by a chemical etchingprocess or by mechanical means.

In one particular embodiment, a turbine component comprising a titaniumbased substrate (20) having a substrate thickness (22), a surface (24),and a bulk hardness may be coated by the presently disclosed method. Thetitanium based substrate (20) may be formed of commercially puretitanium, Ti-6Al-4V, or other titanium based alloys. In this embodiment,a ferromagnetic damping coating (10) layer is affixed to at least aportion of the surface (24) of the titanium based substrate (20),thereby providing a coated substrate (100) and defining acoating-substrate interface. The ferromagnetic damping coating (10) maycomprise one of the ferromagnetic damping materials previously noted.

The ferromagnetic damping coating (10) has a balanced coating residualstress and the balanced coating residual stress includes at least atensile quenching stress component and a compressive peening stresscomponent such that the balanced coating residual stress is within arange of about ±50 MPa. The ferromagnetic damping coating (10) may havea coating thickness (12) of about 2% to about 20% of the substratethickness (22). Moreover, the coated substrate (100) has a damping lossfactor of at least 3.6×10⁻³ at a strain amplitude of 0.0466×10⁻⁴ to7.77×10⁻⁴.

Importantly, the damping loss factor is achievable without having toperform a high temperature annealing process, as previously noted. Byavoiding a high temperature annealing process, the likelihood ofdeveloping a very hard and brittle alpha case layer at thecoating-substrate interface is substantially reduced. As a result, inone embodiment, a hardness of the titanium based substrate (20) at thecoating-substrate interface is within 25% of the bulk hardness (i.e.,the interior hardness) of the titanium based substrate (20). In anotherembodiment, the hardness of the titanium based substrate (20) at thecoating-substrate interface is within 5% of the bulk hardness of thetitanium based substrate (20). The proximity of the hardness valuesindicate that very little, if any, alpha case has formed on the titaniumbased substrate (20). As a result, the turbine component comprising atitanium based substrate (20) is able to be damped by application of aferromagnetic damping coating (10) without having to undergo a hightemperature annealing process, and thereby substantially avoids theformation of unwanted alpha case that can lead to early componentfailure.

Numerous alterations, modifications, and variations of the preferredembodiments disclosed herein will be apparent to those skilled in theart and they are all anticipated and contemplated to be within thespirit and scope of the method for applying a low residual stressdamping coating, as claimed below. For example, although specificembodiments and examples have been described in detail, those with skillin the art will understand that the preceding embodiments and variationscan be modified to incorporate various types of substitute and oradditional or alternative processes and materials, relative arrangementof elements, and dimensional configurations. Accordingly, even thoughonly few variations of the method are described herein, it is to beunderstood that the practice of such additional modifications andvariations and the equivalents thereof, are within the spirit and scopeof the method as defined in the following claims.

1. A method to increase the damping of a substrate (20) having asubstrate thickness (22), comprising: a) heating a ferromagnetic dampingmaterial in powder form such that the ferromagnetic damping material isat least partially molten; b) directing the at least partially moltenferromagnetic damping material at a surface (24) of the substrate (20)at an application velocity such that the at least partially moltenferromagnetic damping material adheres to the surface (24) of thesubstrate (20) and cools to solidification within a solidificationperiod to create a ferromagnetic damping coating (10) on the surface(24) of the substrate (20), resulting in a coated substrate (100); c)wherein the ferromagnetic damping coating (10) has a balanced coatingresidual stress and the balanced coating residual stress includes atleast a tensile quenching stress component and a compressive peeningstress component such that the balanced coating residual stress iswithin a range of ±50 MPa without the coated substrate ever beingsubjected to an annealing temperature of above 700° C. for an annealingperiod of longer than 30 minutes; and d) wherein the ferromagneticdamping coating (10) has a coating thickness (12) of about 2% to about20% of the substrate thickness (22), and the coated substrate (100) hasa damping loss factor of at least 3.6×10⁻³ at a strain amplitude of0.0466×10⁻⁴ to 7.77×10⁻⁴.
 2. The method according to claim 1, whereinthe at least partially molten ferromagnetic damping material is directedat the substrate (20) at an application temperature of at least 800° C.and the application velocity is at least 450 m/s.
 3. The methodaccording to claim 2, wherein the at least partially moltenferromagnetic damping material is directed at the substrate (20) at adamping material deposition rate of at least 30 g/min.
 4. The methodaccording to claim 3, wherein the at least partially moltenferromagnetic damping material is directed at the substrate (20) at adamping material deposition rate of less than 80 g/min.
 5. The methodaccording to claim 1, wherein the ferromagnetic damping material isselected from the group consisting of, by weight percent: about 16percent chromium (Cr), about 1 percent to about 6 percent aluminum (Al),and the balance substantially iron (Fe); and about 16 percent chromium(Cr), about 1 percent to about 4 percent molybdenum (Mo), and thebalance substantially iron (Fe).
 6. The method according to claim 1,wherein the ferromagnetic damping material comprises, by weight percent,about 22 percent to about 38 percent nickel (Ni), and the balancesubstantially cobalt (Co).
 7. The method according to claim 1, whereinthe substrate (20) comprises a component of a turbine.
 8. The methodaccording to claim 7, wherein the component of the turbine comprises atleast one of titanium, titanium-based alloy, steel alloy, nickel,nickel-based alloy, aluminum, and aluminum-based alloy.
 9. A method toincrease the damping of a substrate (20) having a substrate thickness(22), comprising: a) heating a ferromagnetic damping material in powderform such that the ferromagnetic damping material is at least partiallymolten; b) directing the at least partially molten ferromagnetic dampingmaterial at a surface (24) of the substrate (20) at an applicationvelocity of at least 450 m/s such that the at least partially moltenferromagnetic damping material adheres to the surface (24) of thesubstrate (20) and cools to solidification within a solidificationperiod to create a ferromagnetic damping coating (10) on the surface(24) of the substrate (20), resulting in a coated substrate (100); c)wherein the ferromagnetic damping coating (10) has a balanced coatingresidual stress and the balanced coating residual stress includes atleast a tensile quenching stress component and a compressive peeningstress component such that the balanced coating residual stress iswithin a range of about ±50 MPa without the coated substrate (100) everbeing subjected to an annealing temperature of above 700° C. for anannealing period of longer than 30 minutes; and d) wherein theferromagnetic damping coating (10) has a coating thickness (12) of about2% to about 20% of the substrate thickness (22), and the coatedsubstrate (100) has a damping loss factor of at least 3.6×10⁻³ at astrain amplitude of 0.0466×10⁻⁴ to 7.77×10⁻⁴.
 10. The method accordingto claim 9, wherein the at least partially molten ferromagnetic dampingmaterial is directed at the substrate (20) at a damping materialdeposition rate of at least 30 g/min.
 11. The method according to claim10, wherein the at least partially molten ferromagnetic damping materialis directed at the substrate (20) at a damping material deposition rateof less than 80 g/min.
 12. The method according to claim 9, wherein theferromagnetic damping material is selected from the group consisting of,by weight percent: about 16 percent chromium (Cr), about 1 percent toabout 6 percent aluminum (Al), and the balance substantially iron (Fe);and about 16 percent chromium (Cr), about 1 percent to about 4 percentmolybdenum (Mo), and the balance substantially iron (Fe).
 13. The methodaccording to claim 9, wherein the ferromagnetic damping materialcomprises, by weight percent, about 22 percent to about 38 percentnickel (Ni), and the balance substantially cobalt (Co).
 14. The methodaccording to claim 9, wherein the substrate (20) comprises a componentof a turbine.
 15. The method according to claim 14, wherein thecomponent of the turbine comprises at least one of titanium,titanium-based alloy, steel alloy, nickel, nickel-based alloy, aluminum,and aluminum-based alloy.
 16. A turbine component, comprising: a) atitanium based substrate (20) having a substrate thickness (22), asurface (24), and a bulk hardness; and b) a ferromagnetic dampingcoating (10) layer affixed to at least a portion of the surface (24) ofthe titanium based substrate (20), thereby providing a coated substrate(100) and defining a coating-substrate interface, and wherein: i) theferromagnetic damping coating (10) has a balanced coating residualstress and the balanced coating residual stress includes at least atensile quenching stress component and a compressive peening stresscomponent such that the balanced coating residual stress is within arange of about ±50 MPa; ii) the ferromagnetic damping coating (10) has acoating thickness (12) of about 2% to about 20% of the substratethickness (22); iii) the coated substrate (100) has a damping lossfactor of at least 3.6×10⁻³ at a strain amplitude of 0.0466×10⁻⁴ to7.77×10⁻⁴; and iv) a hardness of the titanium based substrate (20) atthe coating-substrate interface is within 25% of the bulk hardness. 17.The turbine component of claim 16, wherein the ferromagnetic dampingcoating (10) comprises a material selected from the group consisting of,by weight percent: about 16 percent chromium (Cr), about 1 percent toabout 6 percent aluminum (Al), and the balance substantially iron (Fe);and about 16 percent chromium (Cr), about 1 percent to about 4 percentmolybdenum (Mo), and the balance substantially iron (Fe).
 18. Theturbine component of claim 16, wherein the ferromagnetic damping coating(10) comprises, by weight percent, about 22 percent to about 38 percentnickel (Ni), and the balance substantially cobalt (Co).
 19. The turbinecomponent of claim 16, wherein the titanium based substrate (20)comprises Ti-6Al-4V alloy.
 20. The turbine component of claim 16,wherein the hardness of the titanium based substrate (20) at thecoating-substrate interface is within 5% of the bulk hardness.